Airborne particles can be significant sources of industrial hazards (e.g., pollutants), health hazards (e.g., biomolecules) and/or public security threats (e.g., chemical and/or biological agents). For this reason, it is desirable to have systems capable of detecting and identifying such particles. The market for such systems is sizable and can extend well beyond government and industrial health and security applications, e.g., the market can extend to air quality monitoring for buildings, inventory inspections, food and drug qualification and authentication applications, etc.
Unfortunately, current systems for detecting and identifying such particles generally rely on gas sensors and are not sufficiently reliable and/or accurate. This is especially true for low vapor pressure particulates, since traditional gas sensors (which are primarily sensitive to gaseous molecules) are generally ineffective for such particulates.
Raman or Fourier transform IR (FTIR) absorption spectroscopy is known to be selective and accurate when it comes to detecting and identifying solids and liquids. However, these analysis techniques generally require a minimum mass of material to analyze. This can be difficult to achieve with airborne particles, and particularly low vapor pressure particulates. Hence, Raman and FTIR spectroscopy has not heretofore been used extensively for detecting and identifying airborne particles.
One possible solution would be to combine a particle concentrator and/or a particle separator with a Raman or FTIR spectroscopic analyzer. However, traditional concentrator geometries (such as conventional electrostatic concentrators or liquid concentrators) generally do not produce a high enough concentration on a surface to be compatible with Raman or FTIR spectroscopy. Furthermore, where the specimen contains multiple particulate species, concentrating enough of the particulates on a surface so as to enable Raman or FTIR spectroscopy can present a new problem, namely, there may be too many different types of airborne species on the analyzer surface, lumped one on top of another. Such lumping of multiple particulate species can make isolation of the individual spectral signatures (and hence identification of the component particulate species) quite difficult.